Apparatus and method for folding a sheet of material

ABSTRACT

An apparatus for folding a sheet of relatively brittle material in which an articulated frame assembly is mounted relative to a support structure in a manner so that two portions of the frame assembly can pivot relative to each other in an angular direction to fold the sheet about a fold line intermediate the ends of the sheet. Each portion of the frame assembly includes a movable portion which is adapted to fold the outer end portion of the sheet about an additional fold line intermediate the first fold lines and the outer edge portion. The sheet is heated along the fold lines prior to the folding operations.

This is a continuation of application Ser. No. 726,263, filed Sept. 24,1976 now abandoned, which is a division of prior application Ser. No.535,980, filed Dec. 23, 1974, now U.S. Pat. No. 4,002,417.

BACKGROUND OF THE INVENTION

This invention relates to an apparatus and method for forming anenvelope from a sheet of a relatively brittle material and, moreparticularly, to such an apparatus and method for forming such anenvelope for use as a battery separator.

Traditionally, wet cell batteries employ at least one pair of oppositepolarity planar electrodes, normally referred to as plates, which areclosely spaced in a parallel relationship and immersed in a liquidelectrolyte to form an electro-chemical couple. A great majority ofthese type batteries employ a plurality of pairs of the oppositepolarity plates with the plates being normally arranged in an upstandingface-to-face relation, and with the exact number of pairs in aparticular battery depending upon the capacity and/or voltage desired.

To avoid adjacent opposite polarity plates from coming into directphysical contact and thereby causing arcing and/or short circuiting, itis necessary to electrically insulate the adjacent plates from eachother. To achieve this insulation, electrically insulative material,usually in the form of sheets similar in size to the electrode plates,and commonly referred to as separators, have been positioned between theopposite polarity plates, with the insulative material being permeableor semipermeable to the liquid electrolyte to sustain the ionicconduction required for the battery action. In older designs, theseparators were formed of rubber, wood, and glass while more recentdesigns have used plastic materials.

Although these types of separators were adequate in many applications,some deficiencies in their insulating capability did develop, especiallyin connection with relatively heavy-duty industrial-type batteries suchas traction batteries, etc. In particular, it has been discovered that,by reason of the close proximity of the exposed side edges of theadjacent plates, dendrites form on and project out from the edge portionof one or the other of the plates, especially after the battery had beenin use for a relatively long period of time. These dendrites causeshort-circuiting and/or arcing between the adjacent plates which, ofcourse, reduces the capacity and/or output voltage of the battery.

In order to overcome this problem, recent battery designs have includedan open ended envelope-type separator of an insulating material whichcovers the side edge portions of the plates and prevents theabove-mentioned short circuiting and arcing.

In a parallel sense, the state of the art has also developed withrespect to the materials used for the separators. In particular, recentdesigns have formed separators of a microporous plastic material,including polyethylene, vinyl resin, and the like, which has excellentinsulating capability yet is relatively low in weight and cost. Anexample of this type of separator is disclosed in U.S. Pat. No.3,696,061, issued Oct. 3, 1972 in the name of Selsor et al., thedisclosure of which is hereby incorporated by reference. The Selsor etal. patent is assigned to the same assignee as the present application.And although battery separators of the type disclosed in theaforementioned Selsor et al. patent have found widespread commercialacceptance, these separators suffer from the disadvantage of beingbrittle and consequently, heretofore have been incapable of being foldedinto the desired envelope configuration on a high production, relativelyinexpensive basis.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide anapparatus and method for forming a relatively brittle plastic sheet intoan envelope.

It is a more particular object of the present invention to provide anapparatus and method for forming an envelope by folding a plastic sheetabout an intermediate fold line and then about two additional fold lineswhile selectively heating the sheet along localized regions thereofdefined essentially by the fold lines to prevent cracking of the sheet.

It is a further object of the present invention to provide an apparatusand method which forms an envelope of the above type suitable for use asa battery separator.

Toward the fulfillment of these and other objects, the apparatus of thepresent invention comprises an articulated support assembly forsupporting the sheet of material, the assembly comprising two portionsadapted for pivotal movement relative to each other to fold the sheetabout a fold line intermediate the ends of the sheet, each portionincluding two members adapted for relative movement for folding thesheet about two additional fold lines each intermediate the first foldline and the end portions of the sheet, and means for selectivelyheating the sheet material along localized regions thereof definedessentially by the fold lines in a sequence corresponding to the foldingoperations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevational view, partially in section, depicting theapparatus of the present invention;

FIGS. 2 and 3 are sectional views taken along the lines 2--2 and 3--3,respectively, of FIG. 1;

FIG. 4 is a partial sectional view taken along the line 4--4 of FIG. 3;

FIG. 5 is a partial rear elevational view of the apparatus of FIGS. 1-4;

FIG. 6 is a schematic diagram of the control system of the apparatus ofthe present invention;

FIGS. 7 and 8 are sectional views of a portion of the apparatus of thepresent invention showing two different operational modes; and

FIG. 9 is a perspective view of the article manufactured according tothe apparatus and method of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1-3 of the drawings, the reference numeral 10 refersin general to a support table formed by front and rear plates 12 and 14,respectively, and a pair of side plates 16 and 18 connected to the frontand rear plates and spaced inwardly from the outer edge portions of thelatter plates. A pair of horizontal plates 20 and 22 are supported in aspaced relationship on the upper edges of the plates 12, 14, 16, and 18.

A pair of spaced parallel rods 24 and 26 extend between the plates 12and 14 inwardly from the plates 16 and 18, and are journalled inbearings 28 extending through the plates 12 and 14, as better shown inFIG. 2, to permit rotation of the rods relative to the plates.

As shown in FIGS. 1 and 2, two pairs of spaced crank levers 30 and 32are fixedly secured to the rods 24 and 26, respectively, and extend in agenerally upward direction from the rods. Two additional pairs of levers34 and 36 are also fixed to the rods 24 and 26, respectively, and extendin a generally downward direction from the rods. The levers 34 and 36are spaced slightly from their corresponding levers 30 and 32 and areattached at their free ends to the ends of two pairs of springs 38 and40, respectively. Two pairs of pins 42 and 44 extend from the plates 16and 18 of the table 10, and are fixed to the other ends of the springs38 and 40, respectively. As a result, the levers 30 and 32 are urged tothe positions shown by the solid lines in FIG. 1 for reasons that willbe explained in detail later. Two pairs of bolts 46 and 48 may bethreadedly mounted relative to the plates 20 and 22 as shown in FIG. 1in order to limit the movement of the crank levers 30 and 32,respectively, in this direction.

As better seen in FIGS. 1 and 3, a pair of spaced parallel rods 50 and52 extend through corresponding openings formed in the levers 30 and 32,respectively, with the rod 50 being journalled at its respective endswithin a pair of spaced parallel arms 54 and 56 which normally extend ina horizontal direction, and the rod 52 being journalled at itsrespective ends within a similar pair of arms 58 and 60.

As shown in FIGS. 2 and 3, the arms 54 and 58 are pivoted at their endsover a pair of eccentric shafts 62 and 64, respectively, extending fromopposite faces of a disc 66 which, in turn, is fixedly secured within asupport assembly 68, by means of a set screw 70 and extending through abase plate 68a of the support assembly and engaging the disc 66. In asimilar manner, the arms 56 and 60 are pivoted at their ends over a pairof eccentric shafts 72 and 74, respectively, extending from a disc 76which, in turn, is fixedly secured with a support assembly 78 by meansof a set screw 79 extending through a base plate 78a of the supportassembly and engaging the disc 76.

An elongated anvil member 80 extends between the base plates 68a and 78aand is bolted at its end portions to the latter plates. As better shownin FIG. 4, the anvil member 80 includes a flange portion 82 extendingfrom its upper surface and along its entire length for reasons that willbe explained in detail later.

Referring to FIGS. 3 and 4, a bar 84 extends between the arms 54 and 56and is bolted at its ends to the free ends of the latter arms, and a bar86 is bolted at its ends to the other ends of the arms 58 and 60. Threespring loaded pins 90 are mounted at spaced intervals in openings formedin the upper surface of the bar 84 and three spring loaded pins 92 aremounted in a similar manner in the bar 86. Each of the spring loadedpins 90 and 92 is urged by its spring to a position where an end portionprojects a relatively small distance outwardly from the correspondingsurfaces of the bars 84 and 86, respectively. Three L-shaped fold bars94 are mounted to the upper surface of the bar 84, and three fold bars96 are mounted to the upper surface of the bar 86. The fold bars 94 and96 have upstanding leg portions 94a and 96a, respectively, for reasonsthat will be explained later.

As shown in FIG. 4, an angle iron support bar 98 is mounted at its endsof the arms 54 and 56 and extends in a spaced parallel relation to thebar 84, while a support bar 100 is mounted in a similar manner to thearms 58 and 60 and in a spaced parallel relation to the bar 86. One legportion of each of a pair of elongated hinge assemblies 102 and 104 ismounted to the support bars 98 and 100, respectively, with the other legportion of each hinge assembly defining a horizontal support surface.

A fold plate 106 extends between the bar 84 and the bar 98 and issupported along its end portions by the pins 90 and by the hingeassembly 102, respectively. In a similar manner, a fold plate 108extends between the bar 86 and the bar 100 and is supported by the pins92 and the hinge assembly 104.

A mandrel, or forming blade, 110 fabricated from a heat-resistant,non-conductive material such as for example, laminated phenolic sheet,is supported above the support table 10 by means of a guide assemblyshown better with reference to FIGS. 1-3. The guide assembly includes apair of vertically extending guide rails 112 and 114 which are bolted tothe inner surface of the rear plate 14 of the support table 10. Each ofthe guide rails 122 and 124 comprises three plates bolted together withan inner plate having a reduced width to define a groove for receiving aslide plate 116. A plurality of bolts 118 attach the slide plate 116 tothe rear face of the forming blade 110 for supporting the blade in theposition shown in FIG. 2.

A pneumatically operated cylinder 120 is supported by a bracket 122located at the top of the guide rails 112 and 114. The cylinder 120 hasa threaded piston rod 124 which is secured in a threaded opening formedin one end portion of a mounting block 126. A notch is formed in theother end portion of the block 126 and receives the upper end portion ofthe slide plate 116. A pin 128 extends through corresponding openingsformed in the mounting block 126 and the slide plate 116 to fix theslide plate relative to the rod 124. Air is selectively admitted anddischarged from the cylinder 120 in a manner to be described later toreciprocally drive the piston rod 124, and therefore the slide plate 116and the forming blade 110, in a generally upwardly and downwardlydirection as viewed in FIG. 2.

A support bracket 129 is secured to the rear of the guide rails 112 and114 and supports an additional pneumatically operated cylinder 130having a piston rod 131. Air is also selectively admitted to anddischarged from the cylinder 120 to reciprocate the rod 131 for reasonsto be described in detail later.

An additional slide plate 132 is slidably disposed in the groove definedbetween the guide rails 112 and 114 below the slide plate 116. Avertical plate 113 is attached to the slide plate 130, extends out ofthe above-mentioned groove, and is connected to a horizontal plate 134which, in turn, is bolted to the base plate 78a of the support assembly78, with the set screw 79 of the latter assembly also extending throughthe plate 134.

As better seen in FIGS. 1 and 2, a threaded rod 136 extends through athreaded opening in a plate 138 affixed to the lower portion of slideplate 116, and is adapted to engage the plate 134, for reasons that willbe explained in detail later.

As shown in FIGS. 2 and 5, a vertically extending plate 140 is mountedto the rear of guide rail 112 and supports three vertically spaced limitswitches 142, 144, and 146, which are sequentially engaged by a blade148 attached to the rear of the slide plate 116 during downward movementof the latter plate. The limit switches 142, 144, and 146 operate tosequentially stop the movement of the slide plate 116, and therefore theforming blade 110, in a manner to be described in detail later.

The piston rod 131 extends through an opening in the blade 148 andreceives a nut 150 which is engaged by the blade at its lowermostposition. As a result, upward movement of the rod 131 by the cylinder130 will also move the blade 148, and therefore the slide plate 116 andthe forming blade 110, in the same direction.

As shown in FIG. 1, a heating element 152, preferably of the electricalimpulse type, is mounted on the folding blade 110 along its lower edgeportion, and a pair of similar heating elements 154 and 156 are mountedon the blade along its upper corners, with the heating elementsfunctioning in a manner to be described in detail later.

The control system for operating the heating elements 152, 154, and 156on the forming blade 110 and the pneumatic cylinders 120 and 130 isshown schematically in connection with FIG. 6. In particular, a controlconsole 160 is provided which has two actuation buttons 162 and 164associated with three timer switches 166, 168 and 170. The timer switch166 is electrically connected, by a conductor 172, to the heatingelement 152, while the timer switch 168 is electrically connected byconductors 174 and 176 to the heating elements 154 and 156,respectively. The timer switch 170 is connected, via a conductor 178, toan air cylinder control unit 180 which operates in a conventional mannerto control the intake and output of air to and from the cylinders 120and 130, respectively, and thus reciprocally drive their respectivepiston rods 124 and 131. In this connection, an additional controlconsole 182 is provided having four actuation buttons 184, 186, 188, and190 which are connected, via lines 192 and 194, to the air cylindercontrol unit 180 to operate the cylinders 120 and 130 in the specificmanner to be described later.

The limit switches 142, 144, and 146 are also electrically connected tothe air cylinder control unit 180 by the lines 196, 198 and 200,respectively, to also control the operation of the cylinders 120 and130.

It will be appreciated that the aforementioned electrical connectionsare part of electrical circuits that are not shown in their entirety inthe interest of brevity, and that such circuits would include variouscomponents such as resistors, relays, etc., as needed to effect theabove operations. The details of these control circuits are conventionaland form no part of the present invention; suffice it to say, that onlythose features thereof which are deemed necessary for a completeunderstanding of the present invention are described herein.

The operation of the apparatus of the present invention will bedescribed in connection with the folding of a workpiece 202 ofrelatively brittle plastic material of the type disclosed, for example,in the above-identified Selsor et al. patent to form the envelope shownin FIG. 9. The workpiece 202 which initially is in the form of arelatively thin, substantially flat sheet is placed over the fold plates106 and 108, which are in their normal horizontal position as shown inFIG. 4, with a piece of relatively soft resilient backing material 204such as, for example, a mat of a silicone sponge rubber, extendingbetween the workpiece and the fold plates. It is noted that the ends ofthe material 204 extend flush with the projecting leg portions 94a and96a, respectively, of the fold bars 94 and 96, and the ends of theworkpiece 202 extend slightly outwardly from or beyond the ends of thematerial 204.

To commence the operation, an operator presses button 184 which, throughthe air cylinder control unit 180, introduces air into the cylinder 120causing its piston rod 124, and therefore the slide plate 116 and theforming blade 110, to move from the position shown in FIG. 2 downwardlyto a position where the rod 136 engages the plate 134, the lower edgeportion of the forming blade engages in an abutting manner the workpiece202 along a line halfway between its two ends and urges this portion ofthe workpiece against the flange 82 of the anvil 80. During thisdownward movement, the end portion of the blade 148 operatively engagesthe limit switch 142 which, through the air cylinder control unit 180,terminates the operation of the air cylinder 120 and therefore stopsmovement of the piston rod 124 and the forming blade 110 in the latterposition.

The operator then pushes the button 162 which actuates the heatingelement 152 and the timer switch 166. The heating element 152 is thusenergized for a predetermined time to apply heat to and therebysoftening that localized region or portion of the workpiece 202 withwhich it is in contact, after which predetermined time the heatingelement is deenergized by the timer switch 166. The operator then pushesbutton 186 which causes the air cylinder 120 to move the forming blade110 further downwardly against the resistance provided by the anvil 80by virtue of the upwardly directed force applied against the anvil bythe springs 38 and 40 acting through the levers 32, 34, 35, 38, the rods54, 56, 58, and 60 and the support assemblies 68 and 78. This movementthrough the action of the support assemblies 68 and 78, the arms 54, 56,58 and 60, and the levers 30 and 32, results in a pivoting movement ofthe arms 54 and 56 about the rod 50, as well as a pivoting movement ofthe arms 58 and 60 about the rod 52 along with movement of the arms 58and 60 about the rod 52 along with movement of the rods 50 and 52.During this movement, the blade 148 engages the limit switch 144, which,through the control unit 180, stops further movement of the formingblade 110 the arms 54, 56, 58 and 60 attain a substantially verticalposition as shown in FIG. 7 and by the dashed line in FIG. 1. Theworkpiece 202 is thus folded about a fold line extending along andwithin the localized region of the workpiece which had been softened bythe heat generated by heater element 152. It is noted that, in theposition of FIG. 7, the fold blades 106 and 108 urge the upper surfacesof the respective corresponding portions of the workpiece 202 againstthe side faces of the forming blade 110.

The operator then presses button 164 which activates the heater elements154 and 156 on the upper edge portions of the folding blade 110, as wellas the timer switches 168 and 170. The heat generated by heater elements154 and 156 thus softens the workpiece 202 along localized regionsspaced slightly inwardly from the ends of the workpiece and aredeactivated after a predetermined time interval by the timer switch 168.The timer switch 170 controls the operation of the air cylinder controlunit in a manner to be described later.

After the heating elements 154 and 156 have been deactivated by thetimer switch 168, the operator then presses button 188 which, throughthe air cylinder control unit 180, causes the air cylinder 120 to movethe forming blade 110 further downwardly a relatively short distanceuntil the blade 148 engages the limit-switch 146 to terminate furthermovement. This movement causes movement of the rods 54 and 56 andtherefore the bar 84 inwardly towards the forming blade 110 and asimilar movement of the rods 58 and 60 and therefore the bar 86, which,in turn, compresses the spring loaded buttons 90 and 92. This, in turn,causes the projecting portions 94a and 96a of the fold bars 94 and 96,respectively, to urge the end portions of the material 204 and thereforethe workpiece 202 outwardly and downwardly as shown in FIG. 8 to foldthem. The timer switch 170, which had been actuated in a previous stepas discussed above, functions, through the control unit 180, to maintainthe assembly in the position shown in FIG. 8 a predetermined time, topermit the workpiece to cool properly. Upon the timer switch 170 turningoff, the operator can push button 190 which actuates the air cylinder130 through the control unit 180, and causes the piston rod 131 to moveupwardly with the nut 150 engaging the blade 148 to force the formingblade 110 to its uppermost position, with this movement being assistedby the springs 38 and 40 and limited by the pins 46 and 48 engaging thelevers 30 and 32, respectively.

The workpiece can then be removed and its folded end portions overlappedto produce the finished product shown in FIG. which is readily adaptableto receive a battery plate, as discussed above. If desired, theoverlapped ends of the envelope may be adhesively secured togetherutilizing known means, such as adhesives, sonic welding techniques, andso on.

It will further be appreciated that the predetermined time intervalscontrolled by the timer switches 166, 168 and during which the heaterelements 152, 154 and 156 are energized will depend upon the thicknessof the workpiece material and the composition of this material. The sameis true with respect to the predetermined time interval controlled bytimer switch 170. Accordingly, these timer switches 166, 168, and 170should be adjustable over a relatively wide range to enable theapparatus of the present invention to accommodate various thicknesses ofvarious materials. In one exemplary embodiment of the invention,polyvinyl chloride based sheets were folded into the envelope shape ofFIG. 9, suitable for use as a battery separator, wherein the sheets hada minimal thickness of about 0.030 inches, the predetermined timinginterval of heating elements 152, 154, and 156 was about 1.5 secondseach, and the cooling-off cycle determined by switch 170 was in therange of about 30 to about 60 seconds. The resulting envelopes exhibitedno sign of cracking in the localized regions corresponding generally tothe fold lines thereof.

Without limiting the present invention, it is thus seen that theapparatus described hereinabove enables a relatively brittle plasticworkpiece to be folded along a plurality of fold lines subsequent tobeing selectively heated in localized regions thereof correspondinggenerally to said fold lines to prevent possible cracking of thematerial, all in a precise yet high-speed and economical manner.

It is understood that variations of the apparatus and method disclosedabove can be made by those skilled in the art without departing from theinvention as defined in the appended claims.

We claim:
 1. A method for forming a sleeve about an elongated foldingblade having four spaced fold lines, said blade having at least threeheaters adjacent respective corners thereof, comprising:(a) disposing asheet of thermoplastics material upon a support table including anelongated anvil member and two rotatable fold plates speced apart onopposite sides of said anvil member; (b) engaging said thermoplasticssheet material between said anvil member and an elongated first heatercharacterized by two spaced corners; (c) heating said sheet materialwith said first heater while said material is engaged between said firstheater and said anvil member; (d) bending the heated said sheet materialabout said spaced corners by rotating said fold plates, forming saidmaterial, about said first heater, into a channel having two sides; (e)heating said sides locally along two regions spaced from said firstheater by two additional heaters of said three heaters; (f) bendingupper portions of each of said sides about corners defined by said twoheaters thereby forming said sleeve.
 2. The method of claim 1 includingengaging said sheet material between said anvil and said bladeapproximately midway between ends of said sheet material.
 3. The methodof claim 1 including cooling said sleeve and removing said sleeve fromsaid blade.
 4. The method of claim 1 wherein each of said two additionalheaters contact said material spaced from ends of said material so thatbends about said additional heaters define a side and said sleeve. 5.The method of claim 4 including forming said material spaced from saidends so as to define said side with end portions of said materialoverlapped.